Low temperature fired electrical components and method of making same

ABSTRACT

A low temperature fired glass-ceramic system encompassing a series of temperature compensating bodies having temperature coefficients that cover a wide range and possessing dielectric constants of from 30 to 125. This system consists of a mixture of a prefired blend of baria, titania and rare earth oxides, and a low firing glass formulation wherein the mixture is fired within the temperature range of 1,800*F to 2,100*F. A slip suspension of this mixture can be used to manufacture monolithic capacitors that utilize a relatively inexpensive palladium-silver electrode.

United States Patent Maher [451 May 21, 1974 LOW TEMPERATURE FIRED ELECTRICAL COMPONENTS AND METHOD OF MAKING SAME Inventor: Galeb II. Maher, Adams, Mass.

Sprague Electric Company, North Adams, Mass.

Filed: Dec. 9, 1971 Appl. No.: 206,402

Related US. Application Data Continuation-impart of Ser. No. 91,706, Nov. 23, 1970, Pat. No. 3,682,766, which is a continuation-in-part of Ser. No. 767,046, Sept. 26, 1968, Pat. Nov 3,619,220, which is a continuation-in-part of Ser. No. 626,245, March 27, l aben sznsd- Assignee:

US. Cl 117/217, 106/39 R, 117/221, 117/227, 317/258, 317/261, 161/196 Int. Cl B44d 1/18, B32b 15/00, H01g 3/07, B32b 17/06 Field of Search 117/217, 221, 219, 227;

[56] References Cited UNITED STATES PATENTS 3,365,631 1/1968 Delaney et a1... 317/258 3,495,996 2/1970 Delaney et a1 317/258 3,515,958 6/1970 Claypoole et a1 317/261 3,292,062 12/1966 Gallagher et a1. 106/39 R 3,368,910 2/1968 Glabau 106/39 R Primary ExaminerCameron K. Weiffenbach [5 7] ABSTRACT 11 Claims, 3 Drawing Figures 'IL/ 1 //T/11///'/////, ll

PATENIEBIM 191 3.81 1.937

LOW TEMPERATURE FIRED ELECTRICAL COMPONENTS AND METHOD OF MAKING SAME CROSS REFERENCES TO RELATED APPLICATIONS The present application is a continuation-in-part of U.S. patent application Ser. No. 91,706 filed Nov. 23, 1970 and issued Aug. 8, 1972 as U.S. Pat. No. 3,682,766, which is a continuation-impart of Ser. No. 767,046 filed Sept. 26, 1968, now U.S. Pat. No. 3,619,220 issued Nov. 9, 1971, which in turn is a continuation-in-part of Ser. No. 626,245 filed Mar. 27, 1967 and later abandoned.

BACKGROUND OF THE INVENTION This invention relates to a low temperature fired glass-ceramic system and a method of making same, and more particularly to components that are made with a low firing glass formulation that is mixed with a ceramic blend containing baria, titania and a rare earth oxide.

Conventional ceramic compositions must be fired to maturity at relatively high temperatures above 2,250F. When a multilayered capacitor employing a high temperature ceramic is formed, the electrodes must be high melting and inert under the capacitor forming conditions. Palladium, one of the platinum group metals employed as the electrode material in this type of a capacitor unit, presently sells for. well over $30.00 per troy ounce. If the capacitor firing temperature can be reduced significantly, without greatly sacrificing capacitance per volume, then the less expensive electrode materials such as silver, which sells for about $1.75 per troy ounce, or silver-palladium alloys can be employed.

Prior art attempts at overcoming this problem have met with limited success. Such success has come however with some sacrifice in dielectric constants and/or with a rather narrow range of temperature coefficients.

Accordingly, it is an object of the present invention to produce a low firing temperature ceramic body that can utilize a relatively inexpensive electrode material and possess characteristics suitable to electrical components.

It is another object of the present invention to provide a low firing temperature ceramic body that has a rather wide range of temperature coefficients and relatively high dielectric constants.

SUMMARY OF THE INVENTION A high temperature ceramic blend and a low firing glass formulation are mixed together and fired at a temperature of between 1,800F and 2,100F. The high temperature ceramic blend is a pre-fired mixture of baria, titania and a rare earth oxide, such as neodymium oxide. For negative temperature coefficient bodies from N200 to Nl000, the high-temperature ceramic is a blend of the pre-fired mixture of baria, titania and the rare earth oxide above plus calcium titanate added thereto. The low firing temperature glass formulation is one containing only CdO, Bi O PbO and at least one of the glass-forming oxides (B or SiO Optimum characteristics, however, are obtained by the inclusion of preferred proportions of the other oxides listed herein. This is the same glass formulation described in the above-mentioned U.S. Pat. Nos. 3,682,766 and 3,619,220. The combination of these compositions together produces a low firing temperature ceramic body that can utilize a relatively inexpensive electrode system and has a range of temperature coefficients of from l000 ppm/"C to +200 ppm/C, with dielectric constants in the range of 125 to 30, respectively.

The rather low firing glass-ceramic composition of the present invention can be employed in forming capacitors, resistors, thermistors, etc., which utilize electrode, resistor or thermistor films of low sintering or low firing temperature materials such as gold, silver, copper, certain silver-palladium alloys, or alloys of any combination thereof.

An electrical component comprising the low temperature fired ceramic body of the present invention will consist essentially of 70 to 92 percent of the high temperature ceramic and 8 to 30 percent of the low firing temperature glass formulation, and will have at least one metallic film located within said body. The metallic film can be a resistance material at the lower end of the firing range, a planar inductance coil, or when at least two metallic films are within said body separated by a layer of said ceramic, the structure will define a capacitor. A component obviously may include all three electrical components.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a ternary diagram of the high temperature composition of the present invention;

FIG. 2 shows a cross-section of a capacitor unit employing the ceramic of this invention; and

FIG. 3 illustrates a microcircuit that is within the scope of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention involves a glass-ceramic system that is fired at a relatively low temperature, and, therefore, can utilize a relatively inexpensive electrode system in electrical components.

The high temperature ceramic system of the dielectric bodies of this invention is either a pre-fired blend of baria, titania and a rare earth oxide, or this pre-fired blend plus a proportion of calcium titanate added thereto. Fully sintered compositions in this ternary system consist, in most cases, of several phases. The compounds of the high temperature ceramic system are present therein in the following amounts (in mole percent): 0-30% baria, 45-95% titania, and 5-50% of a rare earth oxide. The particular amounts will depend on the particular electrical characteristics desired. The pre-fired blend described above maintain its identity through subsequent firings.

The composition of the low firing temperature glass used herein has the following percentage range by This is essentially the glass formulation of the abovementioned U.S. Pat. No. 3,682,766. The preferred percentages of these compounds are as follows:

CdO 36% A1 1% Bi O 23% B 0;, 5% PhD SiO; 5% ZnO 5% A portion of the pre-fired high temperature ceramic ranging from 70 to 92 percent by weight is blended with a portion of the low firing glass formulation ranging from 8 to percent by weight in a suitable organic binder. Amounts of each component part outside of this range will form bodies, but these bodies will not possess the electrical properties desired herein. The blend is ball milled from 6 to 20 hours to achieve grain size in the range of 1 micron. The slurry is then cast, sprayed or drawn in thin layers to form the body desired.

Bodies produced herein, can utilize silver-palladium alloys in the range of 60 to 85% silver and 15 to palladium depending'on the final firing temperature of the glass-ceramic dielectric. Accordingly, ceramic capacitors can be made herein with silver-palladium electrodes that are much less expensive than prior art units made without the low firing glass formulation. The finished body is fired between 1,800F and 2,100F depending on the particular glass-to-ceramic ratios, i.e., the higher the glass content, the lower the firing temperature.

The desired composition of the baria-titania-rare earth oxide is prepared by wet ball milling titanium dioxide with barium carbonate and rare earth hydroxides, hydrates, oxalates, carbonates or oxides for several hours. The slurry is then dried around 150C, gran;

ulated and calcined between 2,250F to 2,600F, depending on the particular composition.

Referring to the drawings, FIG. 1 shows a ternary diagram of the dielectric compositions of the present invention, and gives some examples of the various bodies of the invention. The compositions in F 10. l are shown in the table below:

Composition of High Temp. Ceramic in Mole Example No. TiO BaO Nd,o

, Dielectric Dissipation TCC Example No. Constant Factor ppm/"C l 90 0.5 P500-85O 2 30 0.05 P180 3 68 0.03 NPO 4 52 0.05 P100 5 80 0.06 N100 The TC bodies above cover a range of temperature of 55C to +125C and are described by a number with a letter prefix. The prefix P means a positive temperature coefficient slope where the capacitance will rise with an increase in temperature; N means the capacitance will drop (negative coefficient); and NPO signifies no change. Thus, a designation of N means that for every degree centigrade that the temperature increases, the capacitance will drop 100 parts per million.

FIG. 2 shows a capacitor unit 10 employing the low firing temperature ceramic of this invention wherein metallic film layers 11 are extended into the middle of the capacitor unit from alternate sides separated by layers of the said ceramic material 12 forming a capacitor. The metallic film layers 11 buried within the glassceramic of the present invention is preferably a silverpalladium alloy since the final capacitor is fired at a temperature of between 1,800F-2,100F. The final composition of palladium and. silver going into the body depends on the final firing temperature of the formed body. The final firing temperature is determined by the amounts of glass in the body. So the higher the glass content of the body, the higher percentage of silver in the electrode system. The metallic film layers 11 should have a meltingpoint above the firing temperature of the body, but not substantially greater than the firing temperature. Generally, the maximum firing temperature of the body should always be about 50F below the solidusline of the particular silver-palladium electrode composition used thereon.

In forming an inductor the same low firing temperature ceramic body can be employed and it may or may not contain ferromagnetic material. For a much higher inductance a ferrite or high ferromagnetic system can be employed. A coil pattern of silver, gold, silverpalladium alloys, etc., can be screened on the substrate while it is in the green state and then a top layer of the inventive composition can be applied to form a monolithic inductor.

FIG. 3 shows a microcircuit 13 having ceramic layers l6, l7 and 18 composed of the low firing temperature glass-ceramic of the present invention. Positioned between layers 16 and 17 are inductor l4 and a resistor 15.

In the ternary diagram of FIG. 1, TC bodies other than the examples shown therein can be formed as shown along the extrapolated lines connecting the bodies described, also other compositions within the prescribed semi-circle may be selected for specific applications. TC bodies between, for example, P100 and N100 may be formed by simply mixing desired portions of each of'these calcined high temperature ceramics and subsequently firing this mixture with a portion of the glass. Various portions of each will give TC bodies ranging from P100 to N100. While bodies formed from compositions outside of this semi-circle will have certain electrical properties and characteristics they will not be as advantageous or desirable as those within the semi-circle.

1f negative bodies having high dielectric constants are desired, it has been found that a portion of calcium titanate can be mixed with the'high temperature ceramic after the mixture has been fired and then blended to produce such bodies. For example, 72% (mole percent) of calcium titanate can be added to 28% of the pre-fired blend of Example No. 5 (72.0% TiO 12.0%

BaO, and 16.0% Nd O to form a high temperature ceramic that has a TCC of N750 and has a dielectric constant of 100 and a dissipation factor of 0.05% at l K H Also, 39.0 mole percent of calcium titanate can be added to 61.0 mole percent of the pre-fired blend of 5 Example No. 5 to form a high temperature ceramic that has a TCC of N450 and has a dielectric constant of 85 and a dissipation factor of 0.05% at l K H,.

The negative TC bodies, such as N750 and N450, can be formed without the addition of calcium titanate, however, the dielectric constants of these bodies are considerably lower than those produced with calcium titanate added thereto. It is therefore preferred to add a portion of calcium titanate to the prefired high temperature ceramic before blending with the low firing temperature glass formulation when negative TC bodies that have advantageously high dielectric constants are desired. It should be noted that the pre-fired high temperature ceramic and the calcium titanate react with the glass independently of each other, each maintaining its own identity in the final body.

The high temperature ceramic calcining temperature can be varied depending on the particular electrical properties desired from 2,250F to 2,600F. Separate phases can be calcined individually and then reacted with the glass at lower temperatures (from 1,800F to 2,l00F) depending on the particular glass-to-ceramic ratios. As a general rule, the higher the glass content, the lower the firing temperature of the final body. Preferably, 80 weight percent of the high temperature ceramic and weight percentof the glass are combined to form the final bodies herein.

While neodymium oxide (Nd O is the preferred rare earth oxide for the ternary system, other rare earth compounds can be used with similar, although less desirable, results. However, cerium oxide should be avoided because its electrical properties are not as good as some others. For example, cerium renders the bodies too electrically conductive, lowers the dielectric constant considerably, and produces a higher dissipation factor than when neodymium is used. When lanthanum was mixed with neodymium in equal proportions and used as the rare earth component, similar bodies were formed, but these bodies had slightly lower dielectric constants than the bodies using neodymium as the rare earth component. It should be noted that the rare earth compounds are put into the ternary system as carbonates, hydroxides, hydrates, oxalates, oxides, etc., but upon firing or calcining the net constituents will be the oxides thereof.

it should also be understood that while calcium titanate is preferably added to the high temperature ceramic for producing certain negative TC bodies, other titanates may be used interchangeably with somewhat different results, i.e., lower dielectric constants, or produce less linear temperature coefficient characteristics within the operating temperature range.

In forming a resistor as shown in FIG. 3, any of the well known resistor inks can be employed providing the firing temperature thereof is compatible with the firing temperature of the ceramic substrate. The fabrication of a resistor is very similar to that of'a capacitor. The low firing temperature ceramic slip or paste can be deposited on a temporary substrate to any desired thickness. A metal resistor ink can be screened on in any desired pattern, and a top layer of the low firing temperature slip applied over the resistor ink. The resistor can I be cut to the desired size in the green state and Ag-Pd terminal pick-ups applied thereto. Thereafter, the units can be fired at the lower portion of the given temperature range.

As is evident from the foregoing, the invention is not to be limited to formation of the rather specific illustrative examples. Modifications and variations, as well as the substitution of equivalents may be made without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. An electrical component comprising a low temperature fired ceramic body of a fired blend containing 8 to percent by weight of a low firing temperature glass formulation and 70 to 92 percent by weight of a calcined high temperature ceramic mixture, said glass formulation consisting essentially of CdO 204% A120; 04% Bi,O 18-32% ZnO 04.5% PbO l635% sio 04% 5,0, 040% CaO o 5% 5 -50 moled percent of a rare earth oxide selected from neodymium and/or lanthanum; and at least one metallic film located within said ceramic body, said metallic WIS film having a melting point not substantially greater than the firing temperature of said body.

2. The electrical component of claim 1 wherein said rare earth oxide is neodymium oxide.

3. The electrical component of claim 1 wherein said at least one metallic film is a silver-palladium alloy in the range of 60-85 percent silver and l540 percent palladium.

4. The combination of claim 1 wherein the glass formulation consists essentially of:

CdO 36% A1 0 1% Bi O 23% ZnO 5% PbO 25% SiO 5% B 0 5% 5. The combination of claim 1 wherein said fired blend consists essentially of 20 percent by weight of the low firing temperature glass formulation and percent by weight of the high temperature ceramic mix- 6. The combination of claim 1 wherein said fired blend containsa proportion of calcium titanate.

7. The combination of claim 6 wherein said fired blend consists essentially of 20 percent by weight of the low firing temperature glass formulation and 80 percent by weight of a mixture of saidhigh temperature ce mic. mix ure nd s d ,q l mt tanat making said slurry of from 70 to 92% by weight of said calcined mixture and from 8 to 30% by weight of a low firing glass formulation consisting essentially of CdO 20 40% M 0 2% Bi O; l8 32% ZnO 0 7.5% PbO l6 35% SiO 0 8% B 0; 0 10% CaO 0 in a suitable binder; and

firing said body at a temperature of between 1,800F

and 2,l00F. 9. The method of claim 8 wherein said slurry consists of from 70 to 92 percent by weight of a mixture of calcium titanate and said calcined mixture with from 8 to 30 percent by weight of said low firing glass formula- 8 tion.

10. The method of claim 8 wherein said glass formulation consists essentially of:

CdO 36% M20: 1% Bi O- 23% ZnO 5% PbO 25% sio 5% B20 5% I 

2. The electrical component of claim 1 wherein said rare earth oxide is neodymium oxide.
 3. The electrical component of claim 1 wherein said at least one metallic film is a silver-palladium alloy in the range of 60-85 percent silver and 15-40 percent palladium.
 4. The combination of claim 1 wherein the glass formulation consists essentially of:
 5. The combination of claim 1 wherein said fired blend consists essentialLy of 20 percent by weight of the low firing temperature glass formulation and 80 percent by weight of the high temperature ceramic mixture.
 6. The combination of claim 1 wherein said fired blend contains a proportion of calcium titanate.
 7. The combination of claim 6 wherein said fired blend consists essentially of 20 percent by weight of the low firing temperature glass formulation and 80 percent by weight of a mixture of said high temperature ceramic mixture and said calcium titanate.
 8. A method of forming a low temperature fired ceramic electrical component by forming a body from a slurry with at least one metallic film within said body, and firing said body, wherein the improvement comprises: ball-milling a high temperature ceramic mixture of 0-30 mole percent baria, 45-95 mole percent titania and 5-50 mole percent of a rare earth oxide selected from neodymium and/or lanthanum; calcining said high temperature ceramic mixture at a temperature of between 2,250*F to 2,600*F; making said slurry of from 70 to 92% by weight of said calcined mixture and from 8 to 30% by weight of a low firing glass formulation consisting essentially of
 9. The method of claim 8 wherein said slurry consists of from 70 to 92 percent by weight of a mixture of calcium titanate and said calcined mixture with from 8 to 30 percent by weight of said low firing glass formulation.
 10. The method of claim 8 wherein said glass formulation consists essentially of:
 11. The method of claim 10 wherein said slurry consists of 80 percent by weight of calcium titanate and said calcined mixture and 20 percent by weight of said low firing glass formulation, and said at least one metallic film is a silver-palladium alloy in the range of 60-85% silver and 15-40% palladium. 